Re: [PATCH v3 0/3] qrwlock: Introducing a queue read/write lock implementation

From: Waiman Long
Date: Wed Aug 14 2013 - 11:24:16 EST


On 08/14/2013 06:20 AM, Ingo Molnar wrote:
* Waiman Long<waiman.long@xxxxxx> wrote:


I would like to share with you a rwlock related system crash that I
encountered during my testing with hackbench on an 80-core DL980. The
kernel crash because of a "watchdog detected hard lockup on cpu 79". The
crashing CPU was running "write_lock_irq(&tasklist_lock)" in
forget_original_parent() of the exit code path when I interrupted the
hackbench which was spawning thousands of processes. Apparently, the
remote CPU was not able to get the lock for a sufficient long time due
to the unfairness of the rwlock which I think my version of queue rwlock
will be able to alleviate this issue.

So far, I was not able to reproduce the crash. I will try to see if I
could more consistently reproduce it.
Was it an actual crash/lockup, or a longish hang followed by a lock
detector splat followed by the system eventually recovering back to
working order?

Thanks,

Ingo

It was an actual crash initiated by the NMI handler. I think the system was in a halt state after that.

Regards,
Longman
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